A U.S. district judge in Northern California said that Samsung Galaxy tablets infringe patents held by Apple, but that Apple might find difficulty in establishing the validity of its patents.

According to Reuters, a court session was held earlier today to hear Apple's request to block the sales of some Samsung's Galaxy products from being sold in the United States.

In order for the injunction to be granted, Apple must show that its patents were infringed, but that the patents in question were found to be valid under U.S. law.

U.S. District Judge Lucy Koh said that she would deny Apple's request for a sales embargo based on one of Apple's 'utility' patents -- a legal term to determine how an invention is used. Koh did not say whether an injunction would be grated based on three of Apple's patents relating to the design of the iPad.

In a tweet from the proceedings, Koh "held both tablets above her head, one in each hand". After asking Samsung's lawyers which was which, in an apparent design test, it "took them a while to do so".